Recent popularization of electronic equipments such as digital cameras, smartphones and tablets are increasing the demand for small-sized camera modules. Plastic lenses rather than glass lenses are favorably used in such camera modules. This is because plastic lenses are adaptable to various shapes such as thin lenses and aspherical lenses, inexpensive, and can easily be mass-produced by injection molding.
Highly functional resins have been developed for optical lenses as substitutes for glass and various monomers have been studied as the starting materials thereof. While bisphenol A has mainly served as such a starting material before, polymers made with monomers having fluorene skeletons, for example, 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene (BPEF), have been developed (Patent Literatures 1 and 2). Although such resins having fluorene skeletons have high refractive index and are favorable as an optical material, a polycarbonate resin has much larger thermal expansion coefficient (linear expansion coefficient) than glass, which may cause strain (for example, residual strain after molding). Accordingly, a polycarbonate resin which is useful as an optical material and whose thermal expansion coefficient (linear expansion coefficient) is small has been required.